In steps of producing electronic devices such as liquid crystal displays and CCD/CMOS image sensors, these devices are subjected to a process of being exposed to chemical solutions such as solvents, acid solutions, or alkaline solutions, and/or a process of being exposed to high temperatures, such as sputtering, dry etching, and reflow soldering. To prevent a device from being deteriorated or damaged by such processes, a cured film that is resistant to such processes has been formed on the device as a protection film. Such a protection film is required to be, for example, chemical resistant, highly transparent, and heat resistant.
In cases where the cured film is formed on an uneven surface such as a color filter, a cured film having high planarization properties is needed in order to obtain a process margin in following steps and to obtain the uniform characteristics of a device, for example. A microlens has also been produced from such a cured film.
As one of methods for producing microlenses for CCD/CMOS image sensors, an etch back method has been known (Patent Documents 1 and 2). Specifically, a resist pattern is formed on a resin layer for a microlens formed on a color filter, and the resist pattern is reflowed by a thermal treatment to form a lens pattern. The resin layer for a microlens, which is an underlayer, is subjected to etch back by using as an etching mask, the lens pattern formed by reflowing the resist pattern, and the shape of the lens pattern is transferred to the resin layer for a microlens to produce a microlens.
For example, Patent Documents 3 to 5 describe resin compositions used to form microlenses. However, all of the compositions are photosensitive (radiation sensitive) resin composition, and thus they are not suitable materials for forming microlenses by using the etch back method described above.